Retrofit sound insulation between levels

[Leland S.]

I'm looking to reduce the sound between two levels of a townhome, as I rent them separately, but they were built with standard drywall on the ceiling. The second story is supported by 1.5" open joists. 

After some research, I've come up with the following:

- Blown-in insulation to fill the joists with hard-packed cellulose
- Add asphalt panel board layer across the entire ceiling to the existing drywall and fill the cutouts. 
- Add a second layer of 5/8's drywall to the asphalt board. 

It was suggested that I use sound caulk for a second layer of drywall, but I think the asphalt board will help dampen the lower frequencies more. 

I'll just need 2" screws to reach the old J-boxes in the ceiling for the trimouts. 

I've read the J-boxes also need to be sealed somehow but I'm not sure how. Maybe caulking any gaps or cracks in them should suffice.

Experience appreciated. 

[Chris Seveney]

@Leland S.

This is going to be very costly and the issue it is not resolving is vibratory noise

Having built many building there is sound and vibration transmission - you can dampen the sound (again costly) but if it’s hardwood floors or a kid above it’s not going to stop the pounding / jumping .

Is this a real issue brought by the tenant?

[Leland S.]

Quote from @Chris Seveney:

@Leland S.

This is going to be very costly and the issue it is not resolving is vibratory noise

Having built many building there is sound and vibration transmission - you can dampen the sound (again costly) but if it’s hardwood floors or a kid above it’s not going to stop the pounding / jumping .

Is this a real issue brought by the tenant?

 Yes. Guests provide reviews that noise transmission is high and privacy is low. It is far too transmissible, both vibration and voices/music. I understand vibration cannot be dampened, but I think voices and music would be dampened by this method. 

[Kyle H.]

@Leland S. What is your ceiling height on the ground floor?  I have an up/down duplex where I had the same issue.  We had built the unit ourselves and had done some sound mitigation as well during construction but it ultimately was not sufficient.  We had a 10' ceiling height on the ground floor and ended up dropping a ceiling below the existing floor to decouple the new ceiling from the floor joists.  We ended up just doing a shiplap ceiling to eliminate having to drywall and filled the cavity between the two ceiling with rockwool and it has made a pretty substantial difference that wasn't crazy expensive and was a two day project due to eliminating the need to finish drywall.  

[Leland S.]

That's definitely the best way I'm sure. I have 9ft ceilings, but adding a whole new framing and moving trimouts would be a much bigger job.